The dimensions of the human body require a certain geometry to afford comfort in a sofa or lounge chair. Customarily, seat height is approximately 18 or 19 inches, supportive back height is approximately 14 or 15 inches up from the top of the seat surface, and seat depth is approximately 22 or 23 inches. When the goal is to convert a piece of seating furniture into a sleep surface, these dimensions do not create an adequate sleeping length mattress. To create a standard mattress approximately 78 inches long, many configurations of folded mattress components are possible. The mattress components preferably fit within the body of the piece of seating furniture. To date, when an adequate length sleep surface is achieved, the furniture in its seating mode often can be over-scaled, clumsy and relatively unpleasing in appearance. Also, in order to fit within the furniture piece a mattress of adequate dimensions for a full-size adult to use for sleeping, the mattress's thickness must be reduced to the point of compromising the mattress's comfort.
The unfolding of a cushioned furniture surface to convert, for example, a seating surface into a sleeping surface is currently achieved by unfolding and/or repositioning a supporting frame structure and an accompanying foam cushion. The unfolding or repositioning mechanism may also be used to create a longer seating surface, such as a reclining lounge chair, or for other purposes, such as a doctor's examination table. The unfolding and repositioning of a supporting frame structure is understood in the art and can be accomplished through a variety of known means, including through the use of hinged members, linkages, cables, levers, springs and other simple mechanical devices. Attempts to change the size of elastic foam or cushioned padding, however, present significant problems for a designer.
There are many different types of sofa beds, convertible sofas and other convertible furniture pieces that include a foldable or repositionable frame and a single- or multi-part cushion or mattress positioned within the frame. Basically, the foldable frame and cushion or mattress are configured to fold, rotate, stack and otherwise move so that, in the folded or closed configuration, the cushion or mattress will fit within the volume of the furniture piece and, in the unfolded or open configuration, the cushion or mattress will be supported by the frame and large enough for the intended purpose, for example, sleeping. These convertible furniture pieces, however, can be quite heavy, as the weight of the foldable frame and the associated mechanical linkages and springs—typically of metal—are significant. Several known convertible sofa beds are illustrated in U.S. Pat. Nos. 4,200,941 and 4,176,414.
Other examples of convertible sofa beds incorporate thinner mattresses that can be folded and compressed. The folded and compressed thin mattress then is guided with the portions of the foldable or articulable frame into an interior volume of the sofa bed, typically with at least part of the sofa and frame pivoting upwards and into the interior volume located immediately behind the sofa's back support. This mechanism, however, results in a relatively deep piece of furniture (overall from front to back) when configured in the folded or sitting position, which makes such sofa beds impractical for smaller rooms and aesthetically undesirable. Alternatively, the length of the sleeping surface may extend the length of the sofa, but this results in a sofa with a length (outside arm to opposite outside arm) that is noticeably longer than traditional sofas. Examples of such sofa beds are illustrated in U.S. Pat. Nos. 4,227,268, 4,204,287, 4,086,671, 3,974,529, 3,934,281 and 2,007,988. These and other prior art sofa beds and convertible furniture pieces have generally relied upon folding the foam cushioning, using the frame to reposition it or some combination of the two in order to effect a change in the dimensions of a cushioned or sleeping surface.
In its natural state, any piece of non-rigid, elastic cushioning or foam padding can be compressed or stretched to a certain extent—but with significant, inherent problems. Foam padding that is compressed in length may tend to buckle and bend, and any longitudinal compression may tend to make the foam padding thicker and less compressible in one or more dimensions orthogonal to the direction of compression. Foam padding that is stretched in length does not buckle but may become thinner in one or more dimensions orthogonal to the direction of stretching and then, if stretched too far, will tear or separate. Like many materials, foam padding has a fixed limit of elasticity, and stretching foam beyond this limit results in permanent distortion, deformation, holes or tears in the structure of the foam.
An example of a convertible furniture piece using the compression of non-rigid foam padding is illustrated in U.S. Pat. No. 4,378,609, which shows a sofa bed with a single mattress folded into two sections and then compressed longitudinally to fit the folded sections into the volume beneath and behind the seating cushions typical of a conventional convertible sofa. To compress the mattress once the length is folded in two, the frame includes articulating rigid rails and platforms surrounding the folded foam mattress on all four sides. The non-rigid foam padding is also contained and supported by a rigid platform that acts, in the open position, as a supporting member for the padding and, in the compressed state, as a barrier to contain the compressed foam and prevent buckling or bending in the dimension perpendicular to the direction of compression. The mattress in this construction necessarily is relatively thin so that it not only can be folded onto itself, but also can be compressed within the interior fold of the folded frame. The confinement of the mattress within the interior fold of the folded frame also assists in keeping the mattress from buckling or sliding out of the frame boundaries when it is compressed longitudinally. Because the mattress folds onto itself and then is compressed for storage by being encased in a rigid platform material, the thin mattress may be uncomfortable in the compressed seating configuration because the platform used to contain the foam padding in the compressed state is rigid, thus requiring additional cushions placed on top of the platform for seating. When in the open or unfolded position, the side rails used to contain the cushion in the folded or closed condition also extend upwards from the platform to nearly the top of the foam mattress, resulting in an uncomfortable, rigid edge surrounding the mattress.
Another example of a convertible furniture piece using the compression of non-rigid foam padding is U.S. Pat. No. 6,910,236, which discloses padding with furrows oriented in a direction perpendicular to the direction of compression. As in U.S. Pat. No. 4,378,609, the non-rigid foam padding in U.S. Pat. No. 6,910,236 is also supported on an articulating, rigid base to minimize the buckling of the foam padding when compressed. The patent also discloses the use of a fabric covering secured to the articulating side rails and/or base to contain the remaining three sides of the foam padding during compression. Thus, during compression, the foam padding is confined within a rigid and semi-rigid envelope to reduce the effects of buckling and bending. The foam cushion is also sculpted into a series of furrows or valleys; during compression, the sloping or vertical sides of these valleys in the foam may be pushed together, thereby additionally relieving the tendency of the foam padding to buckle when compressed.
Another approach to convertible furniture is to avoid the use of compressed or stretched foam entirely, as in U.S. Pat. No. 6,904,628, which shows an improved convertible sofa bed with a multiple component mattress having three panels or sections, two of which are folded into a stacked configuration under the seating surface of the sofa and one of which either forms part of the back support of the sofa or folds into an interior volume behind the back support of the sofa. This mechanism permits the use of a thicker and more comfortable mattress material(s), because the mattress is not one contiguous mattress that folds onto itself. Instead, the separate mattress sections pivot and articulate, and one section flips in a reverse direction—so that the mattress sections are located outside of (and are not compressed within) the folded frame. Yet, the mechanism illustrated in this example still uses a relatively large interior volume in the folded, seating or closed orientation, especially below the sofa's seating surface, where two sections of the mattress are stored when folded. The mechanism illustrated in this example also uses a large back support, either formed from part of the mattress or as a fixed surface defining an interior volume where part of the mattress is stored when folded. In either case, the large back support may not be aesthetically desirable.
Improvements to furniture convertible from a “folded,” “storage,” “closed” or “seating” configuration to an “unfolded,” “open” or “sleeping” configuration continue to be sought. In particular, it is desirable to be able to change the size of non-rigid, elastic cushioning or foam padding in a longitudinal dimension while avoiding or minimizing the typical problems associated with folding, compression or elongation of the foam.